Breath alcohol concentration (BrAC) is related to blood alcohol concentration (BAC) by the approximate relation BrAC[mg/1]=0.5*BAC[mg/g]. Other substances will have different coefficients.
Supervised breath tests according to the state of the art are being performed by the police in order to prevent drunk driving. For the same purpose, unsupervised tests using alcolocks in vehicles are also being increasingly used. Sensor technologies include catalytic semiconductors, fuel cells and infrared spectroscopy. Performance with respect to accuracy, specificity, environmental immunity, and response time, is highly variable between different devices available on the market. Devices for breath test include sensor elements providing a signal representing BrAC after taking a deep breath, and emptying the airways via a tight-fitting mouthpiece, which for hygienic reasons has to be a separate, disposable item. In order to ensure a correct determination, the test person is required to deliver a forced expiration at almost full vital capacity. This requires substantial time and effort, especially for persons with limited capacity. The handling of mouthpieces is time-consuming and represents an undesired source of error due to water condensation. The accuracy of the determination represents an increasing challenge, especially when the determination is related to legal limits. Highly accurate breath analyzers for evidential purposes are commercially available, but they are expensive. There is a strong market pull for mass produced devices capable of accurate and reliable breath testing at low cost, and minimum effort for the person to be tested.
The basic techniques of breath analysis were developed during the second half of the 20th century. More recently, a movement towards less obtrusive means for breath test has been noted. Olsson et al (WO 98/20346) disclosed a system solution in which accurate measurements could be performed without a mouthpiece using water vapor as a tracer gas. Lopez (U.S. Pat. No. 5,458,853) reported another approach, using ultrasound to correct for the dependence on distance between the device and the user's mouth. Hök et al (GB 2431470) disclosed a system solution using carbon dioxide (CO2) as a tracer gas, combined with a simple algorithm for correction of a diluted breath sample. Still another approach was reported by Lambert et al (SAE World Congress Apr. 3-6, 2006). The air within a vehicle cabin was monitored, and an alcohol adsorbing material was used to accumulate the sample to enhance resolution. Again, CO2 was used as a tracer gas.